Method and device for cooling a heat generating component

ABSTRACT

The invention relates to a cooling arrangement comprising a heat spreader ( 2 ) comprising a first surface ( 5 ), a second surface ( 8 ), at least one heat absorption chamber ( 9 ) and at least one heat dissipation chamber ( 10 ), the at least one heat absorption chamber ( 9 ) being in thermal contact with the first surface ( 5 ) and the at least one heat dissipation chamber ( 10 ) being in thermal contact with the second surface ( 8 ) and hydraulically coupled to the at least one heat absorption chamber ( 9 ). A cooling fluid ( 13 ) can be driven from the heat absorption chamber ( 9 ) to the heat dissipation chamber ( 10 ) using a plurality of flow patterns for cooling the first surface ( 5 ).

This application is a Division of U.S. Non-Provisional application Ser.No. 12/676,398 filed Nov. 1, 2010 which claims priority toPCT/IB2008/053547 filed Sep. 2, 2008, which claims priority to EuropeanApplication No. 07115962.8, and all the benefits accruing therefromunder 35 U.S.C. §119. The contents of all applications are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a cooling arrangement, an integratedheat spreader and a method for cooling a heat generating component. Moreparticularly, the invention relates to a cooling arrangement comprisinga heat spreader comprising a first surface, a second surface, at leastone heat absorption chamber and at least one heat dissipation chamber,the at least one heat absorption chamber being in thermal contact withthe first surface and the at least one heat dissipation chamber being inthermal contact with the second surface and hydraulically coupled to theat least one heat absorption chamber.

BACKGROUND OF THE INVENTION

Cooling of heat generation components in general and semiconductorcircuits in particular has been an important issue for many years. Withcontinuous increases in transistor density and power consumption ofmicroprocessors, the need for lower cost and more compact microprocessorcooling arrangements has become more desirable to further performanceadvancements. One problem, in particular in microprocessors, is thatheat is generated in a limited physical space. Consequently, foreffective cooling, the heat needs to be spread over a much larger areafor more efficient cooling.

An example of cooling heat generating components is forced airconvection. For example, many processors of current computer systems arecooled by a heat spreader, which distributes the heat generated by theprocessor over a larger surface which is then cooled by forced airconvection using an electric fan.

Patent application US 2007/0017659 A1 discloses a heat spreader having afluid sealed between two plates and a pumping mechanism to actuate amulti-phase flow of the fluid in a planar surface. Thermal energy froman electronic component in contact with the heat spreader is dissipatedfrom a core region via the working fluid to the entire heat spreader andthen to a heat sink. Surface enhancement features located between thetwo plates aid transfer of thermal energy from a first metal plate intothe fluid.

Although improved heat flow from a heat generating component to a muchlarger surface is obtained with the aforementioned technique, achallenge exists to provide even better methods and devices for coolinga heat generating component. In particular, it is desirable that thecooling efficiency of a heat spreader is increased in order that thecooling of even more powerful heat generating components is possible.Conversely, the energy used by a cooling arrangement of a given heatgenerating component should be reduced in order to improve the overallenergy efficiency. In addition, it is a challenge to provide methods anddevices for cooling systems comprising a plurality or network of heatsources with variable loads.

SUMMARY OF THE INVENTION

According to an embodiment of one aspect of the present invention, acooling arrangement is provided. The cooling arrangement comprises aheat spreader comprising a first surface, a second surface, at least oneheat absorption chamber and at least one heat dissipation chamber, theat least one heat absorption chamber being in thermal contact with thefirst surface and the at least one heat dissipation chamber being inthermal contact with the second surface and hydraulically coupled to theat least one heat absorption chamber. The cooling arrangement furthercomprises at least one heat generating component arranged in thermalcontact with the first surface of the heat spreader, a cooling fluid,filling at least part of the heat absorption chamber and the heatdissipation chamber, at least one actuator for driving the coolingfluid, and a controller for generating at least one control signal forthe at least one actuator, such that the cooling fluid can be driventhrough the at least one heat absorption chamber using a plurality offlow patterns.

By providing a heat spreader having a heat absorption chamber and a heatdissipation chamber separate therefrom, the chambers being hydraulicallycoupled to one another, and at least one actuator for driving thecooling fluid, a controlled flow of the cooling fluid through the heatabsorption chamber is generated. Having a separate heat absorptionchamber and heat dissipation chamber reduces the volume of cooling fluidcontained in the heat spreader, thus giving a possibility to avoidreduced pump to heat spreader volume ratios, and may prevent a reductionof the temperature of the fluid on its way to the heat dissipationchamber. Having these components separate also gives more flexibility inmanufacturing and integration by implementing them with modularcomponents.

According to an embodiment of the first aspect, the cooling fluidoscillates between the at least one heat absorption and the at least oneheat dissipation chamber. By having the cooling fluid oscillate betweenthe heat absorption chamber and the heat dissipation chamber, acontrolled movement and exchange of the cooling fluid between the twochambers is implemented, thus transporting heat from the first surfaceto the second surface. In this case, it is preferable that the heatspreader comprises two heat dissipation chambers and at least twoactuators, and the controller is adapted to drive the cooling fluidusing two different flow patterns, wherein, in a first flow pattern, aflow from the first heat dissipation chamber through the at least oneheat absorption chamber to the second heat dissipation chamber iscreated, and, in a second flow pattern, a flow from the second heatdissipation chamber through the at least one heat absorption chamber tothe first heat dissipation chamber is created. In this way, the coolingfluid oscillates between the two heat dissipation chambers, transportingheat to either one in alternating turns, while the heat absorptionchamber is cooled continuously.

Alternatively, the heat spreader preferably comprises four heatdissipation chambers and at least two actuators and the controller isadapted to drive the cooling fluid using four different flow patterns,wherein, in a first flow pattern, a flow from the first heat dissipationchamber through the at least one heat absorption chamber to the thirdheat dissipation chamber is created, in a second flow pattern, a flowfrom the second heat dissipation chamber through the at least one heatabsorption chamber to the fourth heat dissipation chamber is created, ina third flow pattern, the flow from the third heat dissipation chamberthrough the at least one heat absorption chamber to the first heatdissipation chamber is created, and, in a fourth flow pattern, a flowfrom the fourth heat dissipation chamber through the at least one heatabsorption chamber to the second heat dissipation chamber is created.

By using four heat dissipation chambers and four flow patterns, thecooling fluid is pumped through the heat absorption chamber in alternateturns from the first and third heat dissipation chamber and the secondand fourth heat dissipation chamber, respectively. Consequently, while aconstant flow through the heat absorption chamber is generated, part ofthe cooling fluid is always at rest in at least one heat dissipationchamber, where it dissipates its energy.

As a further alternative, the heat spreader preferably comprises amultiplicity of heat dissipation chambers, having a multiplicity ofactuators arranged around the at least one heat absorption chamber in asubstantially radial arrangement and the controller is adapted fordriving the cooling fluid using a multiplicity of different flowpatterns, creating a substantially radial oscillation of a flow of thecooling fluid through the at least one heat absorption chamber.

By creating a radial oscillation in the at least one heat absorptionchamber, the center of the heat absorption chamber is always cooled by aconstant flow of cooling fluid, while part of the cooling fluid storedin one of the multiplicity of heat dissipation chambers is at rest anddissipates the heat transferred from the heat absorption chamber.

According to a further embodiment of the first aspect, the heat spreadercomprises a network of hydraulically interconnected chambers, comprisingthe at least one heat absorption chamber and at least two heatdissipation chambers, the network comprising multiple flow paths, eachflow path connected to at least one actuator, and the controller isadapted to drive the cooling fluid using at least two different flowpaths of the network using the plurality of flow patterns.

By arranging a number of hydraulically interconnected chambers in anetwork, such as an array, heat is transferred using multiple flowsthrough the network between the chambers as desired for more efficientcooling. In particular, by using at least two different heat dissipationchambers, heat can be distributed to alternative heat dissipationchambers in alternating turns associated with the plurality of flowpatterns.

According to a further embodiment of the first aspect, the at least oneheat dissipation chamber comprises at least one membrane coupled to theat least one actuator for actuating the at least one membrane in orderto drive the cooling fluid from or to the at least one heat dissipationchamber. By using a membrane coupled to an actuator, the at least oneheat dissipation chamber acts as a pump for driving the cooling fluid toand from the heat dissipation chamber.

According to a further embodiment of the first aspect, the coolingarrangement comprises at least one first temperature sensor for sensingthe temperature of the heat generating component, the at least one firsttemperature sensor is coupled to the controller, and the controller isadapted to generate the at least one control signal based on the sensedtemperature of the heat generating component. By providing and using afirst temperature sensor for providing feedback from the heat generatingcomponent to the controller, the cooling performance of the coolingarrangement can be adapted to the actual temperature of the heatgenerating component.

In this case, the cooling arrangement preferably further comprises atleast one second temperature sensor for sensing the temperature of theat least one heat dissipation chamber, the at least one secondtemperature sensor is coupled to the controller, and the controller isadapted to generate the at least one control signal based on the sensedtemperature of the at least one heat dissipation chamber. By providingand using a second temperature sensor for providing feedback from theheat dissipation chamber to the controller, the cooling performance ofthe cooling arrangement can be adapted to the actual temperaturedifference between the heat generating component and the heatdissipation chamber.

According to a further embodiment of the first aspect, the heatgenerating component comprises a plurality of areas and associatedtemperature sensors, the plurality of temperature sensors are coupled tothe controller, and the controller is adapted to identify at least onehot spot corresponding to at least one area of the plurality of areas,the at least one hot spot being characterized in that is has atemperature above an average temperature of the plurality of areas, andthe controller is further adapted to generate the at least one controlsignal based on the at least one identified hot spot, such that a flowof cooling fluid is directed to the at least one hot spot in at leastone flow pattern.

By using a multiplicity of temperature sensors for identifying hotspots, a spatial distribution of heat generated by the heat generatingcomponent can be considered by the controller, such that a flow patterndirected to a hot spot is created by the controller.

According to a further embodiment of the first aspect, the heat spreadercomprises a plurality of regions and associated temperature sensors, theplurality of temperature sensors are coupled to the controller, and thecontroller is adapted to identify at least one cold region of the heatspreader, the at least one cold region being characterized in that ithas a temperature below an average temperature of the plurality ofregions, and the controller is further adapted to generate at least onecontrol signal based on the at least one identified cold region, suchthat the flow of cooling fluid is sourced from the at least one coldregion in at least one flow pattern.

By using a multiplicity of temperature sensors for identifying coldregions of the heat spreader, a spatial distribution of heat dissipationof the heat spreader can be considered by the controller, such that aflow pattern sourced from a cold region is created by the controller.

According to a further embodiment of the first aspect, the heat spreadercomprises at least two physically separated flow paths for the coolingfluid and, in a first flow pattern, cooling fluid is driven through theheat absorption chamber using the first flow path and, in a second flowpattern, cooling fluid is driven through the heat absorption chamberusing the second flow path.

By using physically separate cooling paths for the cooling fluid,associated with different flow patterns, cooling fluid used in aparticular flow pattern does not mix with cooling fluid of a separateflow pattern, improving heat distribution in networks of interconnectedheat dissipation and heat absorption chambers.

According to an embodiment of a second aspect of the present invention,an integrated heat spreader is provided. The integrated heat spreadercomprises at least one heat absorption chamber having a first surfacefor interfacing with a heat generating component and at least one heatdissipation chamber having a second surface for interfacing with anexternal coolant, the second surface being larger than the firstsurface. The integrated heat spreader further comprises a cooling fluidfilling, at least partially, the at least one heat absorption chamberand the at least one heat dissipation chamber, at least one fluidinterconnection between the at least one heat absorption chamber and theat least one heat dissipation chamber, and at least one pump element forcreating a plurality of flow patterns between the at least one heatabsorption chamber and the at least one heat dissipation chamber using aforced movement of the cooling fluid.

By providing an integrated heat spreader comprising at least one heatabsorption chamber, at least one heat dissipation chamber, a coolingfluid, at least one fluid interconnection and at least one pump elementfor creating different flow patterns between the chambers, aself-contained cooling system for a heat generating component iscreated.

According to a further embodiment of the second aspect, at least onepump element comprises at least one membrane arranged in the at leastone heat dissipation chamber. By providing a membrane in the at leastone heat dissipation chamber, a pump mechanism internal to theintegrated heat spreader is implemented.

According to a further embodiment of the second aspect, the at least oneheat absorption chamber or heat dissipation chamber comprises at leastone chamber wall having a surface enhancement feature for an increasedheat exchange between the chamber wall and the cooling fluid. A chamberwall having a surface enhancement feature, such as a mesh structure, forexample, increases the thermal flow through the heat spreader.

According to a further embodiment of the second aspect, the heatabsorption chamber comprises at least two physically separated flowpaths for the cooling fluid. By providing at least two physicallyseparated flow paths in the at least one absorption chamber, unintendedmixing of cooling fluid of different flow patterns may be reduced.

According to a further embodiment of the second aspect, the heatabsorption chamber comprises at least four ports for at least four fluidinterconnections, each port hydraulically connected to one further portof the at least four ports of the heat absorption chamber. By connectingeach port of a multi-port heat absorption chamber with only one otherport, a plurality of physically separated flow paths through the heatabsorption chamber is provided.

According to an embodiment of a third aspect of the present invention, amethod for cooling a heat generating component being in thermal contactwith a first surface of a heat spreader having a plurality of chamberscomprising a cooling fluid is provided. The method comprises the stepsof:

determining an average temperature of the first surface or of the heatgenerating component,

determining the position of at least one hot spot of the heat generatingcomponent, the at least one hot spot having a temperature above thedetermined average temperature,

mapping the determined position of the at least one hot spot to alocation on the first surface of the heat spreader,

generating at least one first control signal for generating a first flowpattern of the cooling fluid through the plurality of chambers passingthe mapped location, and

generating at least one second control signal in alternating turns withthe at least first control signal for generating a second flow patternof the cooling fluid through the plurality of chambers, returning thecooling fluid back to its initial location.

By performing the method steps in accordance with the third aspect, anefficient cooling of a hot spot of a heat generating component may beachieved.

According to a further embodiment of the third aspect, in the secondflow pattern the cooling fluid passes the mapped location of the hotspot in alternating turns with the first flow pattern. By also passingthe location mapped to the at least one hot spot in the second flowpattern, a continuous cooling of the hot spot may be achieved.

According to a further embodiment of the third aspect, the methodfurther comprises determining at least one chamber of the plurality ofchambers having a temperature below the determined average temperature,wherein, in the step of generating the at least one first controlsignal, the first flow pattern of the cooling fluid is sourced from theat least one chamber determined to have an below average temperature. Bysourcing the first flow pattern from a chamber having a below averagetemperature, the heat source is cooled to the lowest possibletemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its embodiments will be more fully appreciated byreference to the following detailed description of presently preferredbut nonetheless illustrative embodiments in accordance with the presentinvention when taken in conjunction with the accompanying drawings.

The figures are illustrating:

FIG. 1, a cross-section through a cooling arrangement according to anembodiment of the present invention,

FIG. 2, a cross-section through an integrated heat spreader from aboveaccording to an embodiment of the present invention,

FIG. 3A to FIG. 3D, different flow patterns through a heat absorptionchamber according to different embodiments of the present invention,

FIG. 4, a blade module comprising several heat generating components anda cooling arrangement according to an embodiment of the presentinvention,

FIG. 5, a cross-section through a blade system comprising multipleblades,

FIG. 6, a cross-section through a blade system comprising multiple thinform factor blades,

FIG. 7, a thermal network comprising multiple heat generatingcomponents,

FIG. 8, a heat dissipation chamber having two separate flow pathsaccording to an embodiment of the invention,

FIG. 9, a heat dissipation chamber having four separate flow pathsaccording to an embodiment of the invention, and

FIG. 10, a cooling arrangement using the heat dissipation chamber ofFIG. 8 according to an embodiment of the invention.

In the drawings, the common reference signs are used to refer to likeelements in different embodiments. In addition, added postfixes in theform of characters are used to distinguish individual elements of agroup of similar elements. In cases where no such distinction is made inthe corresponding description, any element of that group may be referredto.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section through a cooling arrangement comprising aprocessor 1, a heat spreader 2 and two actuators 3 a and 3 b. Theactuators 3 are connected to and driven by a controller 19, which may bean integral part of the heat cooling arrangement or the processor 1, orseparate therefrom. The processor 1 is mounted in a socket 4, which alsocomprises electrical contacts for providing the processor 1 withelectrical energy and data. Typically, the processor 1 will comprise alarge number of contacts, for example hundreds of contacts arranged in aso-called ball grid array (BGA). Processor 1 may also be mounteddirectly or indirectly on a printed circuit board (PCB) by any otherknown technology.

The processor 1 has a top surface 5, which is used to dissipate energycreated by the transistors and other circuitry comprised in theprocessor 1. The top surface 5 of the processor 1 is in direct physicaland thermal contact with a first surface 6 of the heat spreader 2. Thetop surface 5 and the first surface 6 roughly match in size and may havean area of roughly 1 cm.sup.2, for example. The heat spreader 2 alsocomprises a multiplicity of air fins 7, which together provide a secondsurface 8. The second surface 8 is much larger than the first surface 6.For example, the second surface 8 may comprise an area of roughly 1000cm.sup.2 with the heat spreader footprint being approximately 100cm.sup.2. The second surface 8 may be cooled by a cooling fan not shownin FIG. 1.

In order to allow fast and efficient heat transfer from the firstsurface 6 to the second surface 8, the heat spreader 2 comprises a heatabsorption chamber 9 and two heat dissipation chambers 10 a and 10 b.The heat absorption chamber 9 and the heat dissipation chambers 10 a and10 b are hydraulically connected by fluid interconnections 11 a and 11b. Actuator 3 a and actuator 3 b can generate a flow from the heatdissipation chamber 10 a through the heat absorption chamber 9 to theheat dissipation chamber 10 b, for example. As can be seen in FIG. 1,the heat absorption chamber 9 is preferably located in physicalproximity to the heat generating component, the processor 1 in thiscase, in order to reduce the thermal resistance there between. In thepresented example, the heat absorption chamber 9 is separated from thetop surface 5 of the processor 1 by a relatively thin chamber wall.

In one example, the actuator 3 a will create an overpressure whileactuator 3 b will create a low-pressure in a cooling fluid 13, fillingat least in part the heat absorption chamber 9 and the heat dissipationchambers 10, resulting in a flow from left to right in the coolingarrangement depicted in FIG. 1. In a subsequent time period, theactuator 3 b may create an overpressure while the actuator 3 a creates alow-pressure such that the cooling fluid 13 flows back from the heatdissipation chamber 10 b through the heat absorption chamber 9 to theheat dissipation chamber 10 a. By moving the cooling fluid 13 from oneheat dissipation chamber 10 a to the other heat dissipation chamber 10b, heat can be transferred with desirable effect from the first surface6 to the second surface 8.

Although FIG. 1 depicts a cooling arrangement comprising two heatdissipation chambers 10 a and 10 b, alternatively a single heatdissipation chamber 10 connected to the heat absorption chamber 9 may beused. For example, a membrane may separate hot and cold cooling fluid 13within a single heat dissipation chamber 10 pumped from and to the heatabsorption chamber 9 using two fluid interconnections 11 a and 11 bsimultaneously. Furthermore, instead of using two actuators 3 a and 3 b,a single actuator 3 and one or more vents may be used to create two ormore different flow patterns through the heat absorption chamber 9.

In the arrangement presented in FIG. 1, both the heat absorption chamber9 and the heat dissipation chambers 10 a and 10 b comprise a meshstructure 12 which increases the internal surface of the chambers andincreases the fluid structure interaction. In consequence, a heattransfer from the solid part of the heat spreader 2, in particular thefirst surface 6, to the cooling fluid 13 and from the cooling fluid 13to the second surface 8 is greatly increased. The mesh structure 12 maybe adapted to the shape and characteristics of each chamber. Forexample, a high density mesh structure 12 may be employed in arelatively small heat absorption chamber 9, while a lower density meshstructure 12 may be employed in a larger heat dissipation chamber 10.

In addition, a solid part 14 of the heat spreader 2 helps to spreadfurther heat from the first surface 6 to the second surface 8. Inparticular in cases where the flow of the cooling fluid 13 is blocked orreduced, a cooling of the processor 1 can be achieved by heat conductionfrom the first surface 6 to the air fins 7 arranged in a central area ofthe heat spreader 2.

FIG. 2 shows a cross-section through an integrated heat spreader 2 fromabove. The heat spreader 2 comprises one heat absorption chamber 9 inthe center and four heat dissipation chambers 10 a to 10 d. The heatabsorption chamber 9 is connected to the four heat dissipation chambers10 a to 10 d by means of fluid interconnections 11 a to 11 d. Each fluidinterconnection 11 comprises an integrated channel structure 15 and atube section 16. The channel structures 15 a to 15 d may be etched orstamped into the solid part 14 of the heat spreader 2. The tube section16 may be bonded to the solid part 14 and the heat dissipation chambers10 a to 10 d.

The different parts of the heat spreader 2 may be comprised in a singleplate as shown in FIG. 1 or in three separate plates, two upper plates17 a and 17 b for heat dissipation and a lower plate 18 for heatabsorption as shown in FIG. 2. That is, the heat spreader 2 may be asingle, integrated physical assembly or a system comprising two or morephysically separate but interconnected units.

The fluid interconnections 11 a to 11 d between the heat absorptionchamber 9 of the lower plate 18 and the four heat dissipation chambers10 a to 10 d of the upper plates 17 a and 17 b may achieve an effectiveheat conductivity which is forty times greater than that of solidcopper, creating a thermal short circuit between the first surface 6,which is in contact with the top surface 5 of a processor 1 or any otherheat generating component, and the second surface 8, for example, fins 7attached to the upper plates 17 a and 17 b cooled by forced airconvection. In addition, by way of the fluid interconnections 11, alower resistance transport of heat to the outermost regions of the heatspreader 2, i.e. away from the heat generating component, may beobtained.

In order to facilitate improved heat transfer from the first surface 6to a cooling fluid 13, a mesh structure 12 may be etched, plated, moldedor stamped into the heat absorption chamber 9. Equally, mesh structures12 may be formed in each one of the heat dissipation chambers 10 a to 10d. The mesh structure 12 integrated into the heat absorption chamber 9may physically connect two opposing walls of that chamber, thus creatingan additional heat conduction path from the first surface 6 to the airfins 7. Such and similar mesh structures 12, also referred to as surfaceenhancement features, are described in further detail in US 2007/0017659A1, which is incorporated herein by reference.

In the example presented in FIG. 2, each of the heat dissipationchambers 10 a to 10 d comprises a membrane 20 which is connected to aninternal or external actuator 3 by means of a piston like element. Bymoving the membrane 20 within a heat dissipation chamber 10 up or down,an over- or low-pressure can be created in that heat dissipationchamber. If, for example, an overpressure is created in the heatdissipation chamber 10 a and an low-pressure is created in the heatdissipation chamber 10 c, the flow of cooling fluid 13 from the heatdissipation chamber 10 a through the fluid interconnection 11 a, theheat absorption chamber 9 and the fluid interconnection 11 c to the heatdissipation chamber 10 c is created. Alternatively, the membranes 20 orother pumping elements may also be located in a separate component fromthe heat dissipation chambers 10.

Assuming that the cooling fluid 13 present at the heat dissipationchamber 10 a is relatively cool, in particular has a temperature below atemperature of the cooling fluid 13 in other regions of the heatspreader 2, a first flow of cooling fluid 13 is created which arrives atfirst surface 6 very rapidly, i.e. using only moderate pump displacementand thus power, and without heating up significantly on its way. The useof moderate pump displacement is achieved due to the low surface tovolume ratio of interconnect 11 a, which is not meshed, in contrast withthe heat exchanging regions 10 a and 9 with a low surface to volumeratio interconnect 11 a. Additionally, the cooling fluid 13, which willbe heated up in the heat absorption chamber 9 to a relatively hightemperature, is transported very effectively to the heat dissipationchamber 10 c without a substantial temperature drop along the narrowfluid interconnection 11 c. Because of the large differences intemperature between the heat absorption chamber 9 and the relativelycool cooling fluid 13 and, inversely, between the relatively warmcooling fluid 13 and the heat dissipation chamber 10 c, heat istransported away from the first surface 6 very rapidly and effectively.

In the example described above, the heated up cooling fluid 13 mayremain at the heat dissipation chamber 10 c temporarily, while a secondflow is created from the heat dissipation chamber 10 b to the heatdissipation chamber 10 d, for example. Using multiple flow patterns hasthe advantage that, while part of the cooling fluid 13 may rest in oneheat dissipation chamber, like heat dissipation chamber 10 c forexample, an uninterrupted flow of cooling fluid 13 through the heatabsorption chamber 9 can be maintained, thus constantly cooling thefirst surface 6 of the heat spreader 2.

The designs of the heat spreaders 2 presented in FIG. 1 and FIG. 2comprise a relatively large solid part 14 and relatively narrow fluidinterconnections 11. In particular, the solid part 14 occupies a largerarea of the presented cross-section of the lower plate 18 than the fluidinterconnections 11. This has the added advantage that even if the flowof cooling fluid 13 is blocked, for example because one or several ofthe actuators 3 is deactivated or fails, because a part of the coolingfluid 13 has escaped from the integrated heat spreader 2 or because oneof the fluid interconnections 11 is blocked, heat dissipation from thefirst surface 6 may still take place by means of heat conduction withinthe solid part 14. Thus, while the overall effectiveness of the heatspreader 2 will be greatly reduced in such cases, limited cooling isstill provided for a heat generating component arranged on the firstsurface 6.

So far, heat dissipation from a heat source spread over a relativelylarge first surface 6 of the heat absorption chamber 9 was described.However, in practice, many heat generating devices have a non-uniformheat distribution along their top surface 5. For example, a processor 1comprises an arithmetic logical unit or processor core and a relativelylarge cache memory, occupying a larger area than the processor core. Theprocessor 1 will generate considerably more heat in the areacorresponding to the processor core than in the area corresponding tothe cache memory. In contrast, the cache memory will occupy most of thearea of the top surface 5 to be cooled. In consequence, a heatgenerating component may comprise one or several so-called “hot spots”,whose temperature is above the average temperature of the heatgenerating component. For example, an arithmetic mean of severaltemperatures measured in different areas of the top surface 5 may bedetermined. An area having a temperature which lies above the determinedarithmetic mean by a predefined absolute or relative amount, for example5 degrees centigrade or a determined standard deviation of the measuretemperatures, is identified as a hot spot. Alternatively, one or severalmaximum values of a temperature distribution may be determined.

FIG. 3A to FIG. 3D show different flow patterns through a heatabsorption chamber 9 which may be used to create effective cooling flowsfor a number of hot spots. In particular, FIG. 3A shows a heatabsorption chamber 9 arranged in the area of a first surface 6. Thefirst surface 6 may correspond, for example, to the die size of asemiconductor chip mounted on the first to surface 6. Fluidinterconnections 11 a to 11 d serve as inlets and outlets to the heatabsorption chamber 9 and are coupled to actuators 3 a to 3 drespectively, although this is not shown in FIG. 3A to FIG. 3D. Inaddition, solid parts 14 separate different flow paths within the heatabsorption chamber 9 and also act as heat conductor and surfaceenhancement features.

In the example shown in FIG. 3A a first flow pattern from fluidinterconnections 11 a and 11 b, acting as fluid inlets, to fluidinterconnections 11 c to 11 d, acting as fluid outlet, is created. Asecond flow pattern, which is not shown in FIG. 3A, is the inverse ofthe fluid pattern presented, i.e. the fluid interconnection 11 c and 11d serve as fluid inlets and the fluid interconnections 11 a and 11 bserve as fluid outlets. Thus, effectively an oscillating flow patternflowing from left to right in a first phase and from right to left in asecond phase through the heat absorption chamber 9 is created.

On the first surface 6, two hot spots 21 a and 21 b are present. Due tothe central solid part 14 and the pressure distribution profile withinthe cooling fluid 13 in the heat absorption chamber 9, a relatively fastfirst flow of cooling fluid 13 across the hot spots 21 a and 21 b iscreated. The first flow has a flow velocity which is above the averageflow velocity of the cooling fluid 13 within the heat absorption chamber9. Relatively cool areas, arranged, for example, between the left,central and right solid parts 14, receive a second flow of cooling fluidhaving a lower flow velocity than the first flow and are not cooled asefficiently by the flow patterns described. In contrast, a much higherpump power would have to be implemented for cooling all areas of thefirst surface 6 equally, resulting in a less effective overall coolingsystem.

FIG. 3B shows a different configuration of a first surface 6 having fourhot spots 21 a to 21 d. Here, a different flow pattern is used to coolthe hot spots 21. In the flow pattern example presented, two opposingfluid interconnections 11 a and 11 d act as fluid inlet, while theremaining fluid interconnections 11 b and 11 c serve as fluid outlets.In the example presented, the flows of cooling fluid 13 are bifurcatedby the central solid part 14 and, in consequence, flows of the coolingfluid 13 across all hot spots 21 a to 21 d are created in a first phase.In a second phase, the direction of the flows indicated in FIG. 3B isreversed, such that fluid inlets 11 a and 11 d serve as fluid outletsand fluid interconnections 11 b and 11 c serve as fluid inlets. Asfurther indicated in FIG. 3B, the axis of the oscillation may be alteredwith time, resulting in a rotating and oscillating flow pattern. Forexample, the axis of oscillation may change from a first diagonaldirection via a horizontal direction and a second diagonal direction toa vertical direction and so on.

FIG. 3C shows a further configuration of a first surface 6 having fourhot spots 21 a to 21 d. In this configuration, the solid part 14arranged in the central area of the heat absorption chamber 9 createsinternal channels 22 a to 22 d. In the configuration shown, the a firstinternal channel 22 a guides cooling fluid 13 across two hot spots 21 aand 21 b while a second internal channel 22 b guides cooling fluid 13across the hot spots 21 c and 21 d.

In a first flow pattern, which is similar to the flow pattern presentedin FIG. 3A, cooling fluid 13 is pumped from the left to the right. In asecond flow pattern, the flow of the cooling fluid 13 is reversed, i.e.a flow from the right to the left is created. Thus, in the first phase,the hot spots 21 a and 21 c are cooled more efficiently, as they areclosest to the fluid inlet. The hot spots 21 b and 21 d are cooled lessefficiently, because by the time the cooling fluid 13 arrives at theirlocation, it has already been pre-heated by the hot spots 21 a and 21 c,reducing its capacity to further absorb heat. In the second phase,inversely, the hot spots 21 b and 21 d are cooled more efficiently, asthey are closest to the fluid inlets.

FIG. 3D shows a further configuration of a heat absorption chamber 9with the first surface 6 comprising eight hot spots 21. In theconfiguration shown in FIG. 3D, two hot spots 21 are present in each oneof the internal channels 22. In addition, the internal channels 22 arenarrower in places of the hot spots 21 than in other places, resultingin an accelerated flow across the hot spots 21. The flow pattern used tocool all of the hot spots 21 are similar to the ones described withreference to FIG. 3B.

Instead of forming discrete internal channels 22 as shown in FIG. 3C andFIG. 3D, a density of a mesh structure 12 may be increased in areasclose to a hot spot 21 and reduced in cooler areas of the first surface.In this way the flow rate of the cooling fluid 13 may be adapted tovarying cooling requirements of a heat generating component.

The physical arrangement of the heat absorption chamber 9 and the fluidinterconnections 11 of FIG. 3A and FIG. 3B and those shown in FIGS. 3Cand 3D are identical. This means that a controller 19 connected to acooling arrangement may switch from one flow pattern, for example alinear flow pattern, to another, for example a radial flow pattern, byadapting one or several control signals provided to actuators 3. Moreparticularly, the situations depicted in FIG. 3A and FIG. 3B, or FIG. 3Cand FIG. 3D may be used for operating the same heat generatingcomponents in different operating modes. For example, a processor 1having multiple processor cores may not use all processor cores at alltimes, resulting in different heat distributions at its top surface 5.

A method for operating the cooling arrangement may be used to computecontrol signals for the actuators 3 that create different flows ofcooling fluid 13 within the heat spreader 2. Such a method can be usedto adapt the configuration of the cooling arrangement on demand. Themethod may be implemented in hard- or software or a combination thereof,e.g. a purpose designed controller 19 or a universal processor 1executing a computer code loaded from some storage medium, like a RAM,ROM or magnetic storage medium.

According to an advanced embodiment, one or several heat sensors arecomprised in the heat generating components, for example on or close toa die of a processor 1, which sense the temperature of the first surface6. This information may be provided to the controller 19 providingsignals to the actuators 3, thus controlling the flow patterns throughthe heat absorption chamber 9. If, for example, a controller 19identifies that the hot spot 21 a shown in the configuration presentedin FIG. 3A is considerably hotter than the hot spot 21 b in the lowerpart, a relatively higher pump drive signal may be provided to theactuators 3 a and 3 c compared with the pump drive signal provided tothe actuators 3 b and 3 d, thus adapting the overall flow patterns usedto the current requirements.

Alternatively, or in addition, temperature sensors may also be providedon or in the heat spreader 2, the heat absorption chamber 9 or the heatdissipation chamber 10. Temperature information provided to thecontroller 19 may be used to identify cooler regions of the heatspreader 2, which may be used as a source of cooling fluid 13 forcooling hot spots 21. In this way, the controller may determine anoptimal configuration automatically, for example by determining the sideof the heat spreader from which cool air or liquid for secondary coolingis provided.

FIG. 4 shows a top view and a cross-section of a so-called blade 26,which is a printed circuit computer board having a particularly thinform factor of roughly 30 mm height. FIG. 4 shows a possibleconfiguration of a heat spreader 2 which is particularly suited forcooling heat generating components of the blade 26. In thisconfiguration, an upper plate 17 comprising a heat dissipation chamber10 is arranged on a cooling plate 23 opposite to a printed circuit board24 carrying one or several heat generating components. The cooling plate23 serves as a heat dissipation area for the arrangement shown in FIG.4, i.e. during operation of the blade 26, heat is transferred from theheat generating components to the cooling plate 23, the heat generatingcomponents having a higher temperature than the cooling plate 23. Theupper plate 17 extends over a large area with respect to the dimensionof the printed circuit board 24 and has a vertical clearance over thehighest surface of components mounted on the printed circuit board 24.

In the example presented in FIG. 4, only a central processor 1 arrangedin the center of the heat spreader 2 is in thermal contact with a firstsurface 6 in an area of a heat absorption chamber 9 of the heat spreader2. The heat absorption chamber 9 is thermally coupled to the coolingplate 23 using a four fluid interconnects 11. In addition, secondaryheat sources 25, such as logic chips, are in thermal contact with airfins 7 made from a heat conductive material, for example copper, whichcouple the secondary heat sources 25 to the upper plate 17.

Membranes 20 and actuators 3 are arranged on the periphery of thecooling plate 23 and can create an oscillating and optionallyazimuthally rotating flow pattern within the upper plate 17. Inaddition, the fluid interconnections 11 create channels between theupper plate 17 and the lower plate 18 comprising the heat absorptionchamber 9 in the area of the processor 1. In this way, hot spots presenton a top surface 5 of the processor 1 can be cooled very effectivelywith a relatively fast flow of cooling fluid 13, while spreading theheat across the extent of the cooling plate 23 having a much largercross sectional area results in a slower flow there.

In addition, cooling may be affected by different means or a combinationthereof. In particular, the blade 26 shown in FIG. 4 may be cooled by anair flow 30 through the air fins 7. In the example presented, the airflow 30 is also used to cool a tertiary heat source 31 having a separatefinned air cooler and memory modules 32. In addition or alternatively,cooling may be performed by heat conduction or radiation from thecooling plate 23, which may be arranged on a chassis part of a bladecage or a further heat exchanger, for example.

FIG. 5 shows a configuration of a computer system comprising severalblades 26. As can be seen in FIG. 5, the cooling plates 23 of blades 26are arranged top-to-top separated by a cold plate 27 of a blade cage 28.The cold plate 27 of the blade cage 28 comprises a secondary coolingcircuit, for example a water cooling system. The cold plate 27 comprisesa coolant having a temperature below the temperature of the coolingplate 23, which transports heat away from the cooling plates 23 of theheat spreader of the blades 26 to an external cooler. At the same time,there is no need for a fluid connection between the blade cage 28 andthe blades 26, allowing straightforward insertion and removal ofindividual blades 26. In this way, a computer system comprising a largenumber of blades 26 can be built and cooled efficiently. Optionally theblades could be arranged bottom-to-top or with higher power dissipationcomponents on both sides of the printed circuit board in order toincrease integration density even further.

FIG. 6 shows another blade system comprising a plurality of so-calledthin form factor blades 26. Thin form factor blades are less than 30 mmin height, such that an arrangement as shown in FIG. 5 may not be usedfor partial air cooling. Thus, according to FIG. 5, practically all theheat dissipated on the printed circuit board 24 is transferred by thecooling fluid 13 from the heat generating components to the cold plate27 directly, i.e. not using a separate lower plate 18 or air fins 7. Inorder to optimize the heat flux from the processor 1, a high densitymesh 12 a is used in its area, acting as a heat absorption chamber 9,while a lower density mesh 12 b is used in another area, acting as aheat dissipation chamber 10. The absorption chamber 9 and thedissipation chambers 10 are combined in one thermal spreader plane thatdistributes the heat load evenly so that it can effectively betransferred across the thermal interface between the spreader and thecold plate 27. With this arrangement, blade components and blade pitchcan be vertically compressed to approximately 5 mm per printed circuitboard with components and thermal spreader planes mounted on both sides.

FIG. 7 shows a thermal network comprising multiple heat sources. In suchan arrangement, multiple heat absorption chambers 9 and heat dissipationchambers 10 may be interconnected by a multiplicity of fluidinterconnections 11. Multiple membrane pumps 29 are connected to thethermal network and allow creating a multiplicity of flow patternsthrough the network. In this way, an array-like structure of heatabsorption chambers 9 and heat dissipation chambers 10 may be controlledeffectively in order to spread the heat generated by a number of heatgenerating components such as processors 1 and secondary heat sources 25over a relatively large area. The heat may be spread uniformly over theentire thermal network or, alternatively, directed to areas withincreased cooling capabilities. For example, higher volumes of coolingfluid 13 may be pumped into a heat dissipating chamber 10 close to acooling air inlet.

Depending on the actual layout of the array, separate membrane pumps 29need not be implemented for each heat dissipation chamber 10. Forexample, a first column, comprising the membrane pump 29 a, the heatdissipation chambers 10 a and 10 c and the heat absorption chamber 9 a,and a second column, comprising the membrane pump 29 b, the heatdissipation chambers 10 b and 10 d and the heat absorption chamber 9 b,are operated together, sharing the two membrane pumps 29 a and 29 b.This is achieved by connecting the lower heat dissipation chambers 10 cand 10 d using a fluid interconnection 11, in particular a tube section16. In this way, while cooling fluid 13 is pumped from the heatdissipation chamber 10 a to the heat dissipation chamber 10 c via afirst heat absorption chamber 9 a, cooling fluid 13 is also pumped fromthe heat dissipation chamber 10 d to the heat dissipation chamber 10 bvia a second heat absorption chamber 9 b.

At the same time, or alternating with this flow of cooling fluid 13, afurther flow pattern corresponding to the row of the network may begenerated by membrane pumps 29 c and 29 d. This will cool the twoprocessors 1 and the two secondary heat sources 25 arranged in that row.The heat absorption chambers 9 c and 9 d may be configured differentlythan the heat absorption chambers 9 a and 9 b, in order to adapt them tothe thermal requirements of the secondary heat sources 25. In theexample presented, they are connected to two fluid interconnections 11,while each one of the heat absorption chambers 9 a and 9 b is connectedto four fluid interconnections 11. In addition, the heat dissipationchambers 10 g and 10 h are smaller than the other heat dissipationchambers 10 shown in FIG. 7, due to the reduced heat generation of thesecondary heat sources 25. In general, instead or additional to adaptingthe flow path used by the cooling fluid 13 in different flow patterns,the amount of cooling fluid 13 pumped through the heat absorptionchambers 9 or heat dissipation chambers may be adapted in different flowpatterns with a controller 19.

FIG. 8 shows an alternative design for a heat absorption chamber 9. Inparticular, the heat absorption chamber 9 according to FIG. 8 comprisestwo separate flow paths 33 a and 33 b, which are physically separatedfrom each other, yet both in thermal contact with a hot spot 21 of theheat absorption chamber 9. The hot spot 21 may be arranged in a centralarea, where the flow paths 33 a and 33 b converge. The heat absorptionchamber 9 comprises four fluid ports 34 a to 34 d, which serve as fluidinlet and fluid outlets to the first and second flow paths 33 a and 33b, respectively.

By actuating the first flow along the first flow path 33 a alternatingwith a second flow along the second flow path 33 b, a radialdistribution of heat from the hot spot 21 is achieved. That is, althoughthe first and second flows are alternating, the hot spot 21 is cooledcontinuously.

FIG. 9 shows a further embodiment of a heat absorption chamber 9according to an embodiment of the invention. In particular, the heatabsorption chamber 9 according to FIG. 9 comprises four separate areas35 a to 35 d that are physically separated from one another by means ofpartitioning walls 36. Each area 35 a to 35 d comprises two fluid ports34, which serve as an inlet and outlet to the particular area.

The embodiment of the heat absorption chamber 9 shown in FIG. 9represents an eight-port radial absorber with four isolated flow paths33. The flow paths 33 according to FIG. 9 are both radially andhorizontally distributed. For example, a first and third flow along theflow paths 33 a and 33 c may be affected in a first flow pattern,whereas a second and a fourth flow of cooling fluid 13 may be affectedin a second flow pattern along flow path 33 b and 33 d.

Alternative control signals may be used to implement more complicatedflow patterns through the heat absorption chamber 9 shown in FIG. 9. Forexample, in a first four-phase flow pattern, each area 35 a to 35 d maybe provided with cooling fluid 13 sequentially around the chamber inphases. In an alternative four-phase flow pattern, the first and thirdareas 35 a and 35 c of the heat absorption chamber 9 may be providedwith a cooling fluid 13 in a first direction in a first phase, followedby the provision of the cooling fluid 13 to the second and the fourtharea 35 b and 35 d in a second phase. In a third and fourth phase, theflow pattern of the first and the second phase are repeated with theinverse orientation of the flow of the cooling fluid 13.

FIG. 10 shows a cooling arrangement using the heat absorption chamber 9according to FIG. 8. The four fluid ports 34 a to 34 d of the heatabsorption chamber 9 are connected to four heat dissipation chambers 10a to 10 d. Using actuators 3 a to 3 d connected with the heatdissipation chambers 10 a to 10 d, in effect a periodic radial spreadingof heat from the heat absorption chamber 9 is implemented by driving theactuators 3 a and 3 c in alternating terms with the actuators 3 b and 3d.

Although different aspects and features of cooling arrangements weredescribed with reference to different embodiments above, a personskilled in the art may combine any feature disclosed herein with anyother feature or combination thereof. In particular, flow patternsdescribed with reference to a single heat absorption chamber 9 may alsobe used in a network or array interconnecting a plurality of heatabsorption chambers 9 and vice versa.

In addition, although the cooling arrangements described above weredescribed with reference to a single plane architecture for reasons ofrepresentational simplicity, the same or similar techniques may beapplied to multi-level design, wherein several heat generatingcomponents are stacked on top of each other, separated by cooling platescomprising one or several heat absorption chambers 9.

1. A cooling arrangement, comprising: a heat spreader comprising a firstsurface, a second surface, at least one heat absorption chamber and atleast one heat dissipation chamber, the at least one heat absorptionchamber being in thermal contact with the first surface and the at leastone heat dissipation chamber being in thermal contact with the secondsurface and hydraulically coupled to the at least one heat absorptionchamber; at least one heat generating component arranged in thermalcontact with the first surface of the heat spreader; a cooling fluid,filling at least part of the heat absorption chamber and the heatdissipation chamber; at least one actuator for driving the coolingfluid; and a controller for generating at least one control signal forthe at least one actuator, such that the cooling fluid can be driventhrough the at least one heat absorption chamber using a plurality offlow patterns.
 2. The cooling arrangement according to claim 1, whereinthe cooling fluid oscillates between the at least one heat absorptionchamber and the at least one heat dissipation chamber.
 3. The coolingarrangement according to claim 2, wherein the heat spreader comprisestwo heat dissipation chambers and at least two actuators, and thecontroller is adapted to drive the cooling fluid using two differentflow patterns, wherein, in a first flow pattern, a flow from the firstheat dissipation chamber through the at least one heat absorptionchamber to the second heat dissipation chamber is created, and, in asecond flow pattern, a flow from the second heat dissipation chamberthrough the at least one heat absorption chamber to the first heatdissipation chamber is created.
 4. The cooling arrangement according toclaim 2, wherein the heat spreader comprises four heat dissipationchambers and at least two actuators and the controller is adapted todrive the cooling fluid using four different flow patterns, wherein, ina first flow pattern, a flow from the first heat dissipation chamberthrough the at least one heat absorption chamber to the third heatdissipation chamber is created, in a second flow pattern, a flow fromthe second heat dissipation chamber through the at least one heatabsorption chamber to the fourth heat dissipation chamber is created, ina third flow pattern, a flow from the third heat dissipation chamberthrough the at least one heat absorption chamber to the first heatdissipation chamber is created, and, in a fourth flow pattern, a flowfrom the fourth heat dissipation chamber through the at least one heatabsorption chamber to the second heat dissipation chamber is created. 5.The cooling arrangement according to claim 2, wherein the heat spreadercomprises a multiplicity of heat dissipation chambers having amultiplicity of actuators arranged around the at least one heatabsorption chamber in a substantially radial arrangement and thecontroller is adapted for driving the cooling fluid using a multiplicityof different flow patterns, creating a substantially radial oscillationof a flow of the cooling fluid through the at least one heat absorptionchamber.
 6. The cooling arrangement according to claim 1, wherein theheat spreader comprises a network of hydraulically interconnectedchambers, comprising the at least one heat absorption chamber and atleast two heat dissipation chambers, the network comprising multipleflow paths, each flow path connected to at least one actuator, and thecontroller is adapted to drive the cooling fluid using at least twodifferent flow paths of the network using the plurality of flowpatterns.
 7. The cooling arrangement according to claim 1, wherein theat least one heat dissipation chamber comprises at least one membranecoupled to the at least one actuator for actuating the at least onemembrane in order to drive to cooling fluid from or to the at least oneheat dissipation chamber.
 8. The cooling arrangement according to claim1, wherein the cooling arrangement comprises at least one firsttemperature sensor for sensing the temperature of the heat generatingcomponent, the at least one first temperature sensor is coupled to thecontroller, and the controller is adapted to generate the at least onecontrol signal based on the sensed temperature of the heat generatingcomponent.
 9. The cooling arrangement according to claim 8, wherein thecooling arrangement further comprises at least one second temperaturesensor for sensing the temperature of the at least one heat dissipationchamber, the at least one second temperature sensor is coupled to thecontroller, and the controller is adapted to generate the at least onecontrol signal based on the sensed temperature of the at least one heatdissipation chamber.
 10. The cooling arrangement according to claim 1,wherein the heat generating component comprises a plurality of areas andassociated temperature sensors, the plurality of temperature sensors arecoupled to the controller, and the controller is adapted to identify atleast one hot spot corresponding to at least one area of the pluralityof areas, the at least one hot spot being characterized in that it has atemperature above an average temperature of the plurality of areas, andthe controller is further adapted to generate the at least one controlsignal based on the least one identified hot spot, such that the flow ofcooling fluid is directed to the at least one hot spot in at least oneflow pattern.
 11. The cooling arrangement according to claim 1, whereinthe heat spreader comprises a plurality of regions and associatedtemperature sensors, the plurality of temperature sensors are coupled tothe controller, and the controller is adapted to identify at least onecold region of the heat spreader, the at least one cold region beingcharacterized in that it has a temperature below an average temperatureof the plurality of regions, and the controller is further adapted togenerate at least one control signal based on the at least oneidentified cold region, such that the flow of cooling fluid is sourcedfrom the at least one cold region in at least one flow pattern.
 12. Thecooling arrangement according to claim 1, wherein the heat spreadercomprises at least two physically separated flow paths for the coolingfluid and, in a first flow pattern, cooling fluid is driven through theheat absorption chamber using the first flow path and, in a second flowpattern, cooling fluid is driven through the heat absorption chamberusing the second flow path.
 13. A cooling arrangement heat spreader,comprising: a solid part having an upper section, a central section, afirst surface at the central section and a tapered section of increasingthickness extending from the upper section to the central section; finsextending away from an upper face of the solid part; heat absorption anddissipation chambers in the central and upper sections to thermallycontact the first surface and the fins, respectively; and fluidinterconnections hydraulically coupling the heat absorption anddissipation chambers and being oriented in parallel with a tapering ofthe tapered section to form obtuse angles with respective planes of theheat absorption and dissipation chambers.
 14. The cooling arrangementheat spreader according to claim 13, further comprising coolant which iscontrollably driven through the heat absorption and dissipation chambersin a plurality of flow patterns.